1. Field of the Invention
The present invention relates to an X-ray moving image radiographing apparatus that captures X-ray radiographic images while a medical professional is providing treatment with respect to a subject.
2. Description of the Related Art
Recently, a technique of Digital Subtraction Angiography (DSA) imaging has become widely used in angiography imaging. DSA imaging is an X-ray radiographing method wherein an X-ray radiographic image is captured before injection of a contrast medium to form a mask image. An X-ray radiographic image is captured after injecting the contrast medium into a blood vessel of a subject, and a background is removed by subtracting the mask image from the contrast medium-injected X-ray radiographic image. Thus, an image of blood vessels to which the contrast medium was injected can be displayed.
An important aspect of DSA imaging is to comprehend a running state of blood vessels. The blood vessels within a human body reside in a three-dimensional space. However, when the blood vessels are subjected to the X-ray radioscopic imaging, information about the blood vessels is compressed into two-dimensional information from three-dimensional information. Consequently, it is difficult to accurately comprehend a running state of the complicated blood vessels by observing a simpler two-dimensional image.
To comprehend the running state of the blood vessel in a three-dimensional manner, a technique of rotation DSA imaging is developed. In rotation DSA imaging, an X-ray radiographic image is captured by an X-ray radiographing apparatus having an X-ray detector. The X-ray detector includes, for example, a C-shaped arm that has an X-ray source disposed on one end and an image intensifier or a flat panel detector (FPD) on the other end. The X-ray radiographing apparatus captures X-ray radiographic images by rotating the C-shaped arm around the subject, to form mask images for every one of rotation angles. After injecting a contrast medium into a blood vessel of the subject, the X-ray radiographing apparatus captures further X-ray radiographic images at the same rotational angles as those used in forming the mask images. Finally, the X-ray radiographing apparatus subtracts the mask images from the X-ray radiographic images of the corresponding rotational angles captured after injection of the contrast medium. Accordingly, moving images of only the blood vessels specified by the contrast medium can be displayed.
Further, in the angiography imaging, when the contrast medium is injected into the blood vessel of the subject, the contrast medium spreads over a wide area at high speed, so that relatively large X-ray detector is required in order to completely capture images of the spreading condition of the contrast medium. Also, it is required to continuously irradiate an X-ray over the entire area where the contrast medium is spreading.
Furthermore, for X-ray radioscopic imaging performed by a catheter or an endoscope, it is may be required to capture images to irradiate the X-ray over a wider area than an area where the catheter or the endoscope is operated.
In addition to the above described X-ray radiographic imaging method, Japanese Patent Application Laid-Open No. 06-217964 discusses a technique relating to an X-ray radiographing apparatus that electronically performs raster scanning in order to detect a focal position of the X-ray.
However, in the rotation DSA imaging, the C-shaped arm needs to be rotated at each time the mask images are captured and the angiography imaging is performed. Since the C-shaped arm is mechanically rotated, an operator must rotate the C-shaped arm with precision. More specifically, the operator needs to pay attention to the C-shaped arm to prevent the arm from striking a table or anything around the C-shaped arm, which may further complicate capturing images. Further, in the angiography imaging, the X-ray is continuously irradiated onto the entire area where the contrast medium is spreading after the injection of the contrast medium, so that X-ray irradiation dosage of the subject is extremely large as well as that of the operator who captures the images. Also, in the X-ray radioscopic imaging using the catheter or the endoscope, the X-ray irradiation dosage of the subject and the operator is extremely large.